Satellite radiotelephone communications systems and methods are widely used for radiotelephone communications. Satellite radiotelephone communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is/are configured to wirelessly communicate with a plurality of satellite radiotelephones and feeder link antennas.
A satellite radiotelephone communications system or method may utilize a single satellite antenna pattern (beam or cell) covering an entire service region served by the system. Alternatively or in combination with the above, in cellular satellite radiotelephone communications systems and methods, multiple satellite antenna patterns (beams or cells) are provided, each of which can serve a substantially distinct service region in an overall service region, to collectively provide service to the overall service region. Thus, a cellular architecture that is similar to that used in conventional terrestrial cellular radiotelephone systems and methods can be implemented in cellular satellite-based systems and methods.
FIG. 1 is a schematic diagram that illustrates a satellite communications system 100 that includes a space based component 102, radioterminals T1-TN, feeder link antennas 110-116 and a gateway processor 120. A network 130 (that may be a wireline and/or wireless network) is also illustrated as being connected to the satellite communications system 100 and may be part of the satellite communications system 100. The radioterminals T1-TN can communicate (through the satellite 102 and feeder link antennas 110-116) with one another and/or with other communications devices that are connected to the network 130. The satellite 102 receives information from the radioterminals T1-TN through return service links, and transmits the information to the feeder link antennas 110-116 through return feeder links. The satellite 102 receives information from the feeder link antennas 110-116 through forward feeder links, and transmits the information to the radioterminals T1-TN through forward service links. In some cases, such as, for example, in broadcasting, a single forward service link of the satellite may communicate information to more than one of the radioterminals T1-TN. The forward feeder links and the return feeder links each use one or more feeder link carriers and/or channels of a feeder link band of frequencies.
To provide a relatively high aggregate signal spectrum from the satellite 102 to one or more satellite gateways (for processing such as, for example, ground-based beam forming), the satellite 102 can be configured to form return feeder link spot beams (antenna patterns) that are aligned with different ones of a plurality of feeder link antennas (i.e., gateway antennas), such as the feeder link antennas 110-116, and can thereby “spatially multiplex” the return service link aggregate spectrum across the return feeder link spot beams to the feeder link antennas 110-116, thereby spatially reusing an available feeder link bandwidth. For example, when the satellite 102 is configured to provide to one or more satellite gateways an aggregate signal spectrum corresponding to, for example, 100 return service link antenna feed elements (of the satellite return service link antenna) with each return service link antenna feed element providing, for example, 20 MHz of spectrum, the satellite 102 must be configured to provide an aggregate of 2 GHz (i.e., 20×100 MHz) of return feeder link spectrum to one or more gateways via one or more respective feeder link antennas, such as, for example, feeder link antennas 110-116, illustrated in FIG. 1. The satellite 102 may be configured to provide the 2 GHz aggregate spectrum while using only a 500 MHz feeder link bandwidth by forming four feeder link spot beams that are aligned with different ones of the four feeder link antennas 110-116, as illustrated in FIG. 1. Because the four feeder link spot beams use the same frequencies within the 500 MHz feeder link spectrum, the feeder link antennas 110-116 must be sufficiently spaced apart geographically to prevent or reduce a level of interference therebetween.
The satellite 102 may also reduce the feeder link bandwidth that is needed to support return service links using the techniques described in U.S. Pat. No. 6,937,857 to the present inventor, entitled Systems And Methods For Reducing Satellite Feeder Link Bandwidth/Carriers In Cellular Satellite Systems, assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. As described in the Abstract of this Patent Application Publication, information content is non-identically mapped between service link carriers and feeder link carriers at a satellite. A reduced number of feeder link carriers compared to the number of service link carriers and/or a reduced total bandwidth of the feeder link carriers compared to the service link carriers may thereby be obtained.
As used herein, the term “radioterminal” includes a cellular and/or satellite radioterminal with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with voice, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet/Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or laptop and/or palmtop computers or other data processing devices, which include a radio frequency transceiver. A radioterminal also may be referred to herein as a “radiotelephone,” a “mobile terminal,” or simply as a “terminal”. As used herein, the term(s) “radioterminal,” “radiotelephone,” “mobile terminal,” and/or “terminal” also include(s) any other communications device, equipment and/or source that may have time-varying or fixed geographic coordinates and/or may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based) and/or situated and/or configured to operate locally and/or in a distributed fashion over one or more terrestrial and/or extra-terrestrial location(s). Furthermore, as used herein, the term “space-based component” or “space-based system” includes one or more satellites at any orbit (geostationary, substantially geostationary, substantially medium earth orbit, substantially low earth orbit, substantially elliptical earth orbit, etc.) and/or one or more other objects and/or platforms (e.g., airplanes, balloons, unmanned vehicles, space crafts, missiles, etc.) that has/have a trajectory above the earth at any altitude.